Newtonian viscosity behavior of dilute to moderately concentrated solutions of cellulose acetate butyrate

The Newtonian viscosity behavior of dilute to moderately concentrated solutions of cellulose acetate butyrate in dioxane was investigated at different temperatures. The viscosity data were analyzed in terms of Martin's and Fedor's relationships and also generalized in terms of reduced variables. The rheological behavior of cellulose acetate butyrate solutions in the whole range of concentrations is determined by the parameter (K_MC [n]). The temperature dependence of viscosities was expressed by the Arrhenius-Frenkel-Eyring equation and the activation energy of viscous flow of polymer solutions (ΔGv) was calculated. ΔGv increases with concentration of polymer solution and is independent of temperature. The preexponential factor, A, related to activation entropy, decreases with concentration of polymer solution. The thermodynamic parameter of viscous flow for cellulose acetate butyrate (CAB)-dioxane solutions is indicative of moderately stiff structure for CAB in solutions.     

Dielectric studies in dilute solutions

Dielectric studies in dilute solutions of cyclohexane and benzene have been carried out in the temperature range 294–318°K. The observed data have been utilized to evaluate the relaxation times and thermodynamic parameters of these molecules. The high values ofα for 2-acetyl pyridine indicate the occurrence of more than one relaxation time. In the remaining systems, the observed lowα values indicate their rigid behaviour. The variation in the dielectric relaxation time is mostly correlated with the change in the heterocyclic configuration of the system.     

pH dependence of electrokinetic behavior of dolomite and magnesite in aqueous electrolyte solutions

In this paper, electrokinetic potential and isoelectric point of dolomite (CaMg(CO₃)₂) and magnesite (MgCO₃) were determined. The effect of various ions such as Mg²⁺, Ca²⁺, Na⁺ and CO₃²⁻ on surface properties of dolomite and magnesite were also examined. Isoelectric points of dolomite and magnesite were determined as 6.3 and 6.8, respectively, in the absence of any electrolyte. H⁺ and OH⁻ ions are the potential determining ions of magnesite and dolomite, as predicted by electrokinetic potential studies.     

Two-dimensional turbulence of dilute polymer solutions

We investigate theoretically and numerically the effect of polymer additives on two-dimensional turbulence by means of a viscoelastic model. We provide compelling evidence that, at vanishingly small concentrations, such that the polymers are passively transported, the probability distribution of polymer elongation has a power law tail: Its slope is related to the statistics of finite-time Lyapunov exponents of the flow, in quantitative agreement with theoretical predictions. We show that at finite concentrations and sufficiently large elasticity the polymers react on the flow with manifold consequences: Velocity fluctuations are drastically depleted, as observed in soap film experiments; the velocity statistics becomes strongly intermittent; the distribution of finite-time Lyapunov exponents shifts to lower values, signaling the reduction of Lagrangian chaos.     

Free energy of electrolyte solutions

The energy of formation of ionic hydrate complexes in infinitely dilute solutions was calculated using the molecular mechanics method. It was found that the OPLS force field is most preferable for calculating the energy of ionic hydration. A correlation relationship between the calculated and experimental energies of ion hydration was derived.     

Submillimeter absorption of electrolyte solutions

Absorption coefficients of very absorbing electrolyte solutions have been measured between 20 and 185 cm^–1. Fourier Transform Spectrometry is used together with a Far Infrared laser spectrometer on a discrete serie of lines. Excess absorption of lithium salts solutions, over that of pure solvent is evidenced for tetrahydrofuran and aqueous solutions.This paper is a part of Bennouna's thesis.     

Irreversible adsorption from dilute polymer solutions

We study irreversible polymer adsorption from dilute solutions theoretically. Universal features of the resultant non-equilibrium layers are predicted. Two broad cases are considered, distinguished by the magnitude of the local monomer-surface sticking rate Q: chemisorption (very small Q) and physisorption (large Q). Early stages of layer formation entail single-chain adsorption. While single-chain physisorption times are typically micro- to milli-seconds, for chemisorbing chains of N units we find experimentally accessible times , ranging from seconds to hours. We establish 3 chemisorption universality classes, determined by a critical contact exponent: zipping, accelerated zipping and homogeneous collapse. For dilute solutions, the mechanism is accelerated zipping: zipping propagates outwards from the first attachment, accelerated by occasional formation of large loops which nucleate further zipping. This leads to a transient distribution of loop lengths s up to a maximum size after time t. By times of order the entire chain is adsorbed. The outcome of the single-chain adsorption episode is a monolayer of fully collapsed chains. Having only a few vacant sites to adsorb onto, late-arriving chains form a diffuse outer layer. In a simple picture we find for both chemisorption and physisorption a final loop distribution and density profile whose forms are the same as for equilibrium layers. In contrast to equilibrium layers, however, the statistical properties of a given chain depend on its adsorption time; the outer layer contains many classes of chain, each characterized by a different fraction of adsorbed monomers f. Consistent with strong physisorption experiments, we find the f values follow a distribution .Received: 13 January 2003, Published online: 8 July 2003PACS: 82.35.-x Polymers: properties; reactions; polymerization - 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion - 68.08.-p Liquid-solid interfaces     

Chirooptical effects in dilute solutions of gelators

The chirooptical properties of a number of compounds in a variety of achiral solvents are studied. The results are interpreted within the framework of the standard model of chiral molecules. It is demonstrated that, with increasing concentration, chiral aggregates emerge, up to the formation of a macrophase (strings), which radically changes the chirooptical characteristics of the solution.     

Utilization of a dilute solid electrolyte in an oxygen gauge

An electrochemical cell involving a SrCl₂-based solid electrolyte either doped or undoped with SrO was investigated. The measuring electrode was of graphite or vitreous carbon and the reference electrode was formed by dissolving Ag⁺ ions and embedding a silver wire. A simple fabrication technique is described. The reported results indicate that an electrode reaction involving dissolved oxide ions: O₂(gas)+4e⁻=2O²⁻ (SrCl₂) can take place and be utilized in an oxygen gauge down to 200°C. The same cell also functions as a chlorinesensor. At least down to 10⁻³ atm, interference with oxygen is negligible.     

Elastic properties of dilute palladium-hydrogen solid solutions

A thin-line pulse-echo technique has been used to measure the variation of the Young's modulus of super-pure palladium as a function of temperature and hydrogen concentration. The resulting measurements have been analyzed so as to yield approximate information relating to the change to be expected in the partial thermodynamic functions of the system due to the lattice relaxation at constant pressure.     

Liquid-liquid interfacial tension of electrolyte solutions

It is theoretically shown that the excess liquid-liquid interfacial tension between two electrolyte solutions as a function of the ionic strength I behaves asymptotically as O(-sqrt[I]) for small I and as O(+/-I) for large I. The former regime is dominated by the electrostatic potential due to an unequal partitioning of ions between the two liquids whereas the latter regime is related to a finite interfacial thickness. The crossover between the two asymptotic regimes depends sensitively on material parameters suggesting that the experimentally accessible range of ionic strengths can correspond to either the small or the large ionic strength regime. In the limiting case of a liquid-gas surface where ion partitioning is absent, the image charge interaction can dominate the surface tension for small ionic strength I such that an Onsager-Samaras limiting law O(-Iln(I)) is expected.     

Counterion phase transitions in dilute polyelectrolyte solutions

In dilute solutions of rodlike polyelectrolytes some counterions are distributed far from polyions while others are located in their vicinity in the regions of cylindrical symmetry of the electrostatic potential. For these cylindrical regions around rodlike polyelectrolytes we find an exact solution of the nonlinear Poisson-Boltzmann equation for the case of nonzero net charge in these regions. This exact solution implies three qualitatively different phases of counterion distribution around the polyions with second order phase transitions between these phases.     

The viscosity of dilute solutions of hard-sphere macromolecules

The Thorne-Enskog theory for the viscosity of dense hard-sphere mixtures is analysed for a dilute suspension of macromolecules. The resulting equation, analogous to the Einstein viscosity equation, shows a dependance of intrinsic viscosity on molecular size which is in accord with observed experimental findings.     

Hydrodynamics of nanoscopic tubulin rings in dilute solutions

We combine fluorescence correlation spectroscopy and sedimentation velocity measurements to probe the hydrodynamic behavior of tubulin dimers and nanoscopic tubulin rings. The rings are rigid, have circular geometry, and are monodisperse in size. We use the high-precision ratio of the sedimentation coefficients and that of the translational diffusion coefficients to validate theories for calculating the hydrodynamic properties of supramolecular structures.